Mechanically Stiff, Electrically Conductive Composites of Polymers and Carbon Nanotubes

ABSTRACT

Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/172,363 filed Apr. 24, 2009entitled “Route to mechanically stiff, electrically conductivecomposites of polymers and carbon nanotubes,” the disclosure of which ishereby incorporated by reference in its entirety for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to and more particularly to a composite ofpolymers and carbon nanotubes, and more particularly, to a mechanicallystiff, electrically conductive composites of polymers and carbonnanotubes.

2. State of Technology

The treatise, Introduction to Nanotechnology, by Charles P. Poole, Jr.,and Frank J. Owens, John Wiley &. Sons, 2003, states: “Nanotechnology isbased on the recognition that particles less than the size of 100nanometers (a nanometer is a billionth of a meter) impart tonanostructures built from them new properties and behavior. This happensbecause particles which are smaller than the characteristic lengthsassociated with particular phenomena often display new chemistry andphysics, leading to new behavior which depends on the size. So, forexample, the electronic structure, conductivity, reactivity, meltingtemperature, and mechanical properties have all been observed to changewhen particles become smaller than a critical size.”

Carbon nanotubes (CNTs) possess a number of intrinsic properties thatmake them promising candidates as filler material in the design of newcomposite systems. CNTs can have electrical conductivities as high as1×10⁶ S m⁻¹, thermal conductivities as high as 3000 W m⁻¹K⁻¹, elasticmoduli of the order of 1 TPa, and are extremely flexible. Unfortunately,the realization of these properties in macroscopic forms, such asconductive polymer/CNT composites, has been limited. In thesecomposites, CNTs are typically dispersed throughout the polymeric matrixby addition of the individual nanotubes or bundles to precursorformulations. Since the loading levels and distribution of the CNTs inthe polymer determine the conductivity of the composite, one of thechallenges associated with the fabrication of conductive polymercomposites is attaining uniform dispersion of the CNTs within thematrix. In addition, dispersion methods can vary greatly depending onthe characteristics of matrix material. While measurable increases inelectrical conductivity can be achieved through addition of as little as0.007 wt % CNTs to polymer matrices, preparation of composites withconductivities >1 S cm⁻¹ requires either higher loadings of CNTs (>10 wt%) or specially-designed CNTs that facilitate dispersion in the matrix.Thus, the fabrication of CNT-polymer composites with conductivities onpar with highly conductive semiconductors and metals for applicationssuch as electromagnetic interference shielding can be an expensiveendeavor. An attractive alternative to the dispersion approach for thedesign of conductive polymer composites would be the use of alow-density, electrically conductive CNT foam as a scaffold that can befilled or infiltrated with the polymer matrix. With this approach, theuniformity of the dispersed phase, and hence the conductivity of thecomposite, is established by the pre-formed CNT network of the scaffold.In addition, this approach could be general and utilized with a widevariety of polymer matrices.

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Many challenges remain in the effort to realize the exceptionalmechanical and electrical properties of carbon nanotubes in compositematerials. Applicants have developed highly electrically conductive andmechanically stiff composites of polymers and single-walled carbonnanotubes (SWNT). Conductive SWNT-based nanofoams (aerogels) are used asscaffolds to create polymer [poly(dimethylsiloxane)] composites. Theresulting composites possess electrical conductivities over 1 S cm⁻¹ andexhibit an ˜300% increase in the elastic modulus with as little as 1 vol% nanotube content.

DEFINITION OF TERMS

Various terms used in this patent application are defined below.

-   -   CA=Carbon Aerogel    -   CNT=Carbon Nanotubes    -   CA-CNT=Carbon Aerogel & Carbon Nanotube Composite    -   Nanofoam=Aerogel    -   SWNT=Single-Walled Carbon Nanotubes    -   DWNT=Double-Walled Carbon Nanotubes    -   SDBS=Sodium Dodecylbenzene Sulfonate    -   MESOPORPOUS=Pore Dia. 2 & 5 mm    -   PVA=Polyvinyl Alcohol    -   CVD=Chemical Vapor Deposition    -   TEM=Transmission Electron Microscopy    -   SEM=Scanning Electron Microscopy    -   R/C=Resorcinol to Catalyst Ratios    -   RF=Resorcinol and Formaldehyde Solids    -   BET=Brunauer-Emmett-Teller    -   Mechanically Robust=Can withstand strains greater than 10%        before fracture    -   Electrically Conductive=Exhibits an electrical conductivity of        10 S/m or greater    -   Mechanically Stiff=Elastic modulus greater than 10 MPa    -   Ultralow-Density=Exhibits densities less than 50 mg/cc    -   Carbon Nanotube-Based Aerogel=Porous carbon material consisting        of 5 to 95% carbon nanotubes by weight    -   SWNT-CA=Single-Walled Carbon Nanotubes/Carbon Aerogel    -   PDMS/SWNT-CA=Polydimethylsiloxane (PDMS)/Single-Walled Carbon        Nanotubes/Carbon Aerogel

Applicants used SWNT-CAs as scaffolds to fabricate stiff, highlyconductive polymer (PDMS) composites via the infiltration method withlittle to no degradation of the conductive network of the CNT-basedscaffold. Conductivities as high as 1 S cm⁻¹ have been observed for SWNTloadings as low as 1 vol % (1.2 wt %) in polymer/SWNT-CA composites. Inaddition to excellent electrical conductivity, the polymer compositeexhibited an ˜300% increase in Young's modulus, producing not only ahighly conductive, but a stiffer composite as well. The exceptionalproperties of this polymer composite and the general nature of thefabrication method provide the potential for a whole new class ofcomposites based on the SWNT-CA scaffold.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIGS. 1A, 1B, 1C, and 1D are SEM images under different magnificationsof conductive PDMS/SWNT-CA composites.

FIGS. 2A and 2B show partial load-displacement curves for PDMS andPDMS/CNT composite.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to the drawings, to the following detailed description, and toincorporated materials, detailed information about the invention isprovided including the description of specific embodiments. The detaileddescription serves to explain the principles of the invention. Theinvention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Applicants synthesized ultralow-density SWNT-based foams (SWNT-CA) withexceptional electrical and mechanical properties. In these foams, carbonnanoparticles were used as a binder to crosslink randomly orientedbundles of single-walled CNTs. These SWNT-CAs simultaneously exhibitedincreased stiffness and high electrical conductivity even at densitiesapproaching 10 mg cm⁻³. The foams are stable to temperatures approaching1000° C. and have been shown to be unaltered by exposure to extremelylow temperatures during immersion in cryogenic liquids (such as liquidhydrogen). Therefore, in addition to use as catalyst supports, sensors,and electrodes, these ultra-light and robust foams can serve asscaffolds for the preparation of novel CNT composites. As the conductivenetwork is already established, the CNT foam can simply be impregnatedthrough the wicking process with the matrix of choice, ranging frominorganic sols to polymer melts to ceramic pastes, to prepare a varietyof conductive CNT composites. Applicants used SWNT-CA foam scaffolds forthe synthesis of a highly conductive poly(dimethylsiloxane) (PDMS)composite. This polymer composite exhibits ˜300% increase in the elasticmodulus relative to the unloaded PDMS elastomer and electricalconductivity over 1 S cm⁻¹, the highest conductivity reported for apolymer/SWNT composite at this CNT loading level (1.2 wt % or 1 vol %).

Method of Preparation

SWNT-CA nanofoams, with a SWNT loading of 55 wt % (1 vol %) and amonolith density of 28 mg cm⁻³, were prepared as described in:

(1) Co-Pending patent application Ser. No. 12/652,616 titled“Mechanically Robust, Electrically Conductive Ultralow-Density CarbonNanotube-Based Aerogels,” filed Jan. 5, 2009 which is incorporatedherein in its entirety by this reference;

(2) the journal article, “Mechanically robust and electricallyconductive carbon nanotube foams,” by Marcus A. Worsley, Sergei O.Kucheyev, Joe H. Satcher, Jr., Alex V. Hamza, and Theodore F. Baumann,in APPLIED PHYSICS LETTERS 94, 073115 (2009) which is incorporatedherein in its entirety by this reference; and

(3) “Properties of single-walled carbon nanotube-based aerogels as afunction of nanotube loading,) by Marcus A. Worsley, Peter J.Pauzauskie, Sergei O. Kucheyev, Joseph M. Zaug, Alex V. Hamza, Joe H.Satcher Jr., and Theodore F. Baumann, in Acta Materialia 57 (2009)5131-5136, which is incorporated herein in its entirety by thisreference.

Once the SWNTs are dispersed, organic sol-gel chemistry is usedcrosslink the CNT bundles. Typically, organic sol-gel chemistry involvesthe polymerization of organic precursors to produce highly crosslinkedorganic gels that can be dried and pyrolyzed to yield porous carbonstructures. In this case, low concentrations of the sol-gel precursors(resorcinol, formaldehyde) and catalyst (sodium carbonate) are added tothe CNT suspension to induce polymerization primarily on the walls ofthe CNT bundles and, more importantly, at the junctions between adjacentbundles to form an organic binder.

The resulting gel is then dried and subsequently pyrolyzed to convertthe organic binder to carbon, yielding the SWNT-CA nanofoam. The volumepercent of SWNTs in each sample was calculated from the initial mass ofSWNTs added, a CNT density of 1.3 g cm⁻³, and the final volume of thesample. The synthesis process for the SWNT-CA allows for a range ofpossible shapes and sizes. SWNT-CA right cylinders with diameters of ˜1cm and heights of ˜2 cm have been fabricated.

Composites were prepared by immersing the as-prepared SWNT-CA in thepolymer resin prior to cure. The immersed SWNT-CA is placed under vacuumuntil no more air escaped from the scaffold, suggesting fullinfiltration of the resin. The infiltrated SWNT-CA is then cured at 60°C. to produce the composite. The dimensions of the composite areapproximately equal to those of the initial SWNT-CA.

Referring now to the drawings and in particular to FIGS. 1A, 1B, 1C, and1D, scanning electron microscopy (SEM) images of PDMS/SWNT-CA compositesshow that the SWNTs are homogenously distributed throughout the polymermatrix, suggesting that there is good wetting at the PDMS/SWNT-CAinterface and that the CNT-based scaffold is intact after infiltrationand curing. FIG. 1A is a SEM image under low magnification of theconductive PDMS/SWNT-CA composite. FIG. 1B is a SEM image under highmagnification of the conductive PDMS/SWNT-CA composite.

TABLE 1 Physical properties of SWNT-CA scaffold, polymers and conductivepolymer composites CNT (vol %), Density/g Material (wt %) cm⁻³ E/MPa /Scm⁻¹ SWNT-CA 1, 55  0.028 1.0 1.12 PDMS 0, 0  1.04 4.2 <0.001PDMS/SWNT-CA  1, 1.2 1.01 14 1.00

This observation is supported by the fact that the electricalconductivity of the SWNT-CA scaffold is maintained even in a fully denseinsulating matrix as shown by Table 1. To Applicant's knowledge, theconductivity of these polymer composites (1 S cm⁻¹) represents thehighest conductivity reported for a polymer/SWNT composite prepared atsuch a low CNT loading level (1.2 wt % or 1 vol %). Interestingly, theelectrical conductivity of this composite is on par with the highestreported value for a polymer/MWNT at a similar ˜1 wt % MWNT loading. AsSWNTs typically contain some fraction of semiconducting tubes, ascompared to MWNTs, which presumably are all metallic, one might expect ahigher conductivity in the MWNT composite with similar CNT loadings.This observation highlights the need for further study in this area andsuggests that even larger improvements in the conductivity of polymercomposites are possible.

Referring now to FIGS. 2A and 2B, nanoindentation measurements show thatthe PDMS/SWNT-CA experiences very elastic behavior with an ˜300%increase in Young's modulus as compared to the case of PDMS. Theobserved enhancement in modulus is consistent with the increase expectedbased on the Halpin-Tsai model for a nanotube bundle aspect ratio of˜100. A similar increase in modulus was observed by Dyke and Tour for aPDMS/SWNT composite prepared with 1 wt % loading ofsurface-functionalized SWNT. The improved modulus is also consistentwith the observation of a polymer shell that coats the CNT bundles inthe SEM images as shown in FIG. 1. The presence of the polymer shellsuggests strong bonding at the PDMS/SWNT-CA interface, a key element insuccessful reinforcement. These results highlight the effectiveness ofusing a pre-made CNT scaffold for structural reinforcement.

Example 1

SWNT-CA nanofoams, with a SWNT loading of 55 wt % (1 vol %) and amonolith density of 28 mg cm⁻³, were prepared as previously reported.Briefly, purified SWNTs were suspended in deionized water and thoroughlydispersed via sonication.

Once the SWNTs were dispersed, organic sol-gel chemistry was usedcrosslink the CNT bundles. Typically, organic sol-gel chemistry involvesthe polymerization of organic precursors to produce highly crosslinkedorganic gels that can be dried and pyrolyzed to yield porous carbonstructures. In this case, low concentrations of the sol-gel precursors(resorcinol, formaldehyde) and catalyst (sodium carbonate) were added tothe CNT suspension to induce polymerization primarily on the walls ofthe CNT bundles and, more importantly, at the junctions between adjacentbundles to form an organic binder.

The resulting gel was then dried and subsequently pyrolyzed to convertthe organic binder to carbon, yielding the SWNT-CA nanofoam. The volumepercent of SWNTs in each sample was calculated from the initial mass ofSWNTs added, a CNT density of 1.3 g cm⁻³, and the final volume of thesample. The synthesis process for the SWNT-CA allows for a range ofpossible shapes and sizes. In this report, SWNT-CA right cylinders withdiameters of ˜1 cm and heights of ˜2 cm were fabricated.

Composites were prepared by immersing the as-prepared SWNT-CA in thePDMS polymer resin prior to cure. The immersed SWNT-CA was placed undervacuum until no more air escaped from the scaffold, suggesting fullinfiltration of the resin. The infiltrated SWNT-CA was then cured at 60°C. to produce the composite. The dimensions of the composite wereapproximately equal to those of the initial SWNT-CA.

Materials and Methods

Materials. All reagents were used without further purification.Resorcinol (99%) and formaldehyde (37% in water) were purchased fromAldrich Chemical Co. Sodium carbonate (anhydrous) was purchased from J.T. Baker Chemical Co. Highly purified SWNTs were purchased from CarbonSolutions, Inc.

SWNT-CA preparation. The SWNT-CAs were prepared using traditionalorganic sol-gel chemistry [1]. In a typical reaction, purified SWNTs(Carbon Solutions, Inc.) were suspended in deionized water andthoroughly dispersed using a VWR Scientific Model 75T Aquasonic (sonicpower ˜90 W, frequency ˜40 kHz). The concentration of SWNTs in thereaction mixture was 1.3 wt %. Once the SWNTs were dispersed, resorcinol(1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol) and sodiumcarbonate catalyst (5.95 mg, 0.056 mmol) were added to the reactionsolution. The resorcinol-to-catalyst ratio (R/C) employed was 200. Theamount of resorcinol and formaldehyde (RF solids) used was 4 wt %. Thesol-gel mixture was then transferred to glass molds, sealed and cured inan oven at 85° C. for 72 h. The resulting gels were then removed fromthe molds and washed with acetone for 72 h to remove all the water fromthe pores of the gel network. The wet gels were subsequently dried withsupercritical CO2 and pyrolyzed at 1050° C. under a N2 atmosphere for 3h. The SWNT-CAs materials were isolated as black cylindrical monoliths.Foams with a SWNT loading of 55 wt % (1 vol %) were prepared by thismethod.

Characterization. Scanning electron microscopy (SEM) characterizationwas performed on a JEOL 7401-F at 5-10 keV (20 mA) in secondary electronimaging mode with a working distance of 2-8 mm. Electrical conductivitywas measured using the four-probe method with metal electrodes attachedto the ends of cylindrical samples. The amount of current transmittedthrough the sample during measurement was 100 mA, and the voltage dropalong the sample was measured over distances of 3 to 6 mm. Seven or moremeasurements were taken on each sample, and results were averaged.Mechanical properties were studied by indentation in an MTS XPNanoindenter with a Berkovich diamond tip. A series of both continuousand partial load-unload indents (with 5 cycles and an unloadingpercentage of 100% for each cycle) was carried out in laboratory air atroom temperature. The loading rate was continuously adjusted to keep aconstant representative strain rate of 10⁻³ s⁻¹, defined as(dP/dt)cotè/4P, where P is load, t is time, and è=72.1° is theequivalent cone angle of the Berkovich tip used. For every cycle, theunloading rate was kept constant and equal to the maximum loading rateof the cycle. The Oliver-Pharr method [2] was used to analyze partialload-unload data in order to calculate the indentation elastic modulusas a function of the indenter penetration.

Example 2

SWNT-CA nanofoams, with a SWNT loading of 55 wt % (1 vol %) and amonolith density of 28 mg cm⁻³, were prepared as previously reported.Briefly, purified SWNTs were suspended in deionized water and thoroughlydispersed via sonication.

Once the SWNTs were dispersed, organic sol-gel chemistry was usedcrosslink the CNT bundles. Typically, organic sol-gel chemistry involvesthe polymerization of organic precursors to produce highly crosslinkedorganic gels that can be dried and pyrolyzed to yield porous carbonstructures. In this case, low concentrations of the sol-gel precursors(resorcinol, formaldehyde) and catalyst (sodium carbonate) were added tothe CNT suspension to induce polymerization primarily on the walls ofthe CNT bundles and, more importantly, at the junctions between adjacentbundles to form an organic binder.

The resulting gel was then dried and subsequently pyrolyzed to convertthe organic binder to carbon, yielding the SWNT-CA nanofoam. The volumepercent of SWNTs in each sample was calculated from the initial mass ofSWNTs added, a CNT density of 1.3 g cm⁻³, and the final volume of thesample. The synthesis process for the SWNT-CA allows for a range ofpossible shapes and sizes. In this report, SWNT-CA right cylinders withdiameters of ˜1 cm and heights of ˜2 cm were fabricated.

Composites were prepared by immersing the SWNT-CA in the epoxy polymerresin prior to cure. The immersed SWNT-CA was placed under vacuum untilno more air escaped from the scaffold, suggesting full infiltration ofthe resin. The infiltrated SWNT-CA was then cured at elevatedtemperature of 150° C. to produce the epoxy/SWNT-CA composite.

Materials and Methods

Materials. All reagents were used without further purification.Resorcinol (99%) and formaldehyde (37% in water) were purchased fromAldrich Chemical Co. Sodium carbonate (anhydrous) was purchased from J.T. Baker Chemical Co. Highly purified SWNTs were purchased from CarbonSolutions, Inc.

SWNT-CA preparation. The SWNT-CAs were prepared using traditionalorganic sol-gel chemistry [1]. In a typical reaction, purified SWNTs(Carbon Solutions, Inc.) were suspended in deionized water andthoroughly dispersed using a VWR Scientific Model 75T Aquasonic (sonicpower ˜90 W, frequency ˜40 kHz). The concentration of SWNTs in thereaction mixture was 1.3 wt %. Once the SWNTs were dispersed, resorcinol(1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol) and sodiumcarbonate catalyst (5.95 mg, 0.056 mmol) were added to the reactionsolution. The resorcinol-to-catalyst ratio (R/C) employed was 200. Theamount of resorcinol and formaldehyde (RF solids) used was 4 wt %. Thesol-gel mixture was then transferred to glass molds, sealed and cured inan oven at 85° C. for 72 h. The resulting gels were then removed fromthe molds and washed with acetone for 72 h to remove all the water fromthe pores of the gel network. The wet gels were subsequently dried withsupercritical CO2 and pyrolyzed at 1050° C. under a N2 atmosphere for 3h. The SWNT-CAs materials were isolated as black cylindrical monoliths.Foams with a SWNT loading of 55 wt % (1 vol %) were prepared by thismethod.

Characterization. Scanning electron microscopy (SEM) characterizationwas performed on a JEOL 7401-F at 5-10 keV (20 mA) in secondary electronimaging mode with a working distance of 2-8 mm. Electrical conductivitywas measured using the four-probe method with metal electrodes attachedto the ends of cylindrical samples. The amount of current transmittedthrough the sample during measurement was 100 mA, and the voltage dropalong the sample was measured over distances of 3 to 6 mm. Seven or moremeasurements were taken on each sample, and results were averaged.

TABLE 2 Material CNT, vol % (wt %) σ, Scm⁻¹ Epoxy 0 <0.001 Epoxy/SWNT-CA1 (1.2) 1.01

Additional information about Applicants' invention is disclosed in thejournal article, “Stiff and electrically conductive composites of carbonnanotube aerogels and polymers,” by Marcus A. Worsley, Sergei O.Kucheyev, Joshua D. Kuntz, Alex V. Hamza, Joe H. Satcher, Jr., TheodoreF. Baumann, in J. Mater. Chem., 2009, 19, 3370-3372. The J. Mater.Chem., 2009, 19, 3370-3372, is incorporated herein in its entirety bythis reference.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of making a stiff and electrically conductive composite ofcarbon nano tube aerogel and polymer, comprising the steps of: providinga single-walled carbon nanotubes carbon aerogel, immersing saidsingle-walled carbon nanotube carbon aerogel in a polymer resin toproduce a single-walled carbon nanotubes carbon aerogel infiltrated withsaid polymer resin, and curing said single-walled carbon nanotubescarbon aerogel infiltrated with said polymer resin to produce the stiffand electrically conductive composite of carbon nanotube aerogel andpolymer.
 2. The method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer of claim 1 wherein saidstep of immersing said single-walled carbon nanotube carbon aerogel in apolymer resin to produce a single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin includes placing said single-walledcarbon nanotube carbon aerogel immersed in a polymer resin under vacuum.2. The method of making a stiff and electrically conductive composite ofcarbon nanotube aerogel and polymer of claim 1 wherein said step ofcuring said single-walled carbon nanotubes carbon aerogel infiltratedwith said polymer resin to produce the stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer comprises curing saidsingle-walled carbon nanotubes carbon aerogel infiltrated with saidpolymer resin at 60 or 150° C.
 3. The method of making a stiff andelectrically conductive composite of carbon nanotube aerogel and polymerof claim 1 wherein said step of providing a single-walled carbonnanotubes carbon aerogel comprises providing SWNT-CA nanofoams with aSWNT loading of 55 wt % (1 vol %) and a monolith density of 28 mg cm⁻³.4. The method of making a stiff and electrically conductive composite ofcarbon nanotube aerogel and polymer of claim 1 wherein said step ofimmersing said single-walled carbon nanotube carbon aerogel in a polymerresin to produce a single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin comprises immersing saidsingle-walled carbon nanotube carbon aerogel in polydimethylsiloxaneresin.
 5. The method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer of claim 4 wherein saidstep of curing said single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin comprises curing said single-walledcarbon nanotubes carbon aerogel infiltrated with saidpolydimethylsiloxane resin to produce the stiff and electricallyconductive composite of carbon nanotube aerogel and polymer.
 6. Themethod of making a stiff and electrically conductive composite of carbonnanotube aerogel and polymer of claim 1 wherein said step of immersingsaid single-walled carbon nanotube carbon aerogel in a polymer resin toproduce a single-walled carbon nanotubes carbon aerogel infiltrated withsaid polymer resin comprises immersing said single-walled carbonnanotube carbon aerogel in epoxy polymer resin.
 7. The method of makinga stiff and electrically conductive composite of carbon nanotube aerogeland polymer of claim 4 wherein said step of curing said single-walledcarbon nanotubes carbon aerogel infiltrated with said polymer resincomprises curing said single-walled carbon nanotubes carbon aerogelinfiltrated with said epoxy polymer resin to produce the stiff andelectrically conductive composite of carbon nanotube aerogel andpolymer.
 8. The method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer of claim 1 wherein saidstep of immersing said single-walled carbon nanotube carbon aerogel in apolymer resin to produce a single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin comprises immersing saidsingle-walled carbon nanotube carbon aerogel in polydimethylsiloxane orepoxy resin.
 9. The method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer of claim 4 wherein saidstep of curing said single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin comprises curing said single-walledcarbon nanotubes carbon aerogel infiltrated with saidpolydimethylsiloxane or epoxy resin to produce the stiff andelectrically conductive composite of carbon nanotube aerogel andpolymer.
 10. A method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer, comprising the stepsof: dispersing nanotubes in an aqueous media or other media to form asuspension, adding reactants and catalyst to said suspension to create areaction mixture, curing said reaction mixture to form a wet gel, dryingsaid wet gel to produce a dry gel, pyrolyzing said dry gel to produce asingle-walled carbon nanotubes carbon aerogel, immersing saidsingle-walled carbon nanotube carbon aerogel in a polymer resin toproduce a single-walled carbon nanotubes carbon aerogel infiltrated withsaid polymer resin, and curing said single-walled carbon nanotubescarbon aerogel infiltrated with said polymer resin to produce the stiffand electrically conductive composite of carbon nanotube aerogel andpolymer.
 11. The method of making a stiff and electrically conductivecomposite of carbon nanotube aerogel and polymer of claim 10 whereinsaid step of immersing said single-walled carbon nanotube carbon aerogelin a polymer resin to produce a single-walled carbon nanotubes carbonaerogel infiltrated with said polymer resin includes placing saidsingle-walled carbon nanotube carbon aerogel immersed in a polymer resinunder vacuum.
 12. The method of making a stiff and electricallyconductive composite of carbon nanotube aerogel and polymer of claim 10wherein said step of curing said single-walled carbon nanotubes carbonaerogel infiltrated with said polymer resin to produce the stiff andelectrically conductive composite of carbon nanotube aerogel and polymercomprises curing said single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin at 60 or 150° C.
 13. The method ofmaking a stiff and electrically conductive composite of carbon nanotubeaerogel and polymer of claim 10 wherein said step of providing asingle-walled carbon nanotubes carbon aerogel comprises providingSWNT-CA nanofoams with a SWNT loading of 55 wt % (1 vol %) and amonolith density of 28 mg cm⁻³.
 14. A mechanically stiff, electricallyconductive composite of polymer and carbon nanotubes comprising: aporous carbon material having 5 to 95% by weight carbon nanotubes and 5to 95% carbon binder, and a polymer infiltrated within said porouscarbon material having 5 to 95% by weight carbon nanotubes and 5 to 95%carbon binder.
 15. The mechanically stiff, electrically conductivecomposite of polymer and carbon nanotubes of claim 14 wherein saidpolymer infiltrated within said porous carbon material having 5 to 95%by weight carbon nanotubes and 5 to 95% carbon binder ispolydimethylsiloxane or epoxy.
 16. A mechanically stiff, electricallyconductive composite of polymers and carbon nanotubes comprising: amechanically stiff, electrically conductive composite prepared by themethod of providing a single-walled carbon nanotubes carbon aerogel,immersing said single-walled carbon nanotube carbon aerogel in a polymerresin to produce a single-walled carbon nanotubes carbon aerogelinfiltrated with said polymer resin, and curing said single-walledcarbon nanotubes carbon aerogel infiltrated with said polymer resin toproduce the stiff and electrically conductive composite of carbonnanotube aerogel and polymer.